Curable compositions

ABSTRACT

A heat-curable composition is disclosed comprising a hydroxyl-bearing polymer; a liquid, polyglycol hemi-formal diluent; and an aminoplast or phenolic resin capable of curing the hydroxyl-bearing polymer. Optionally, a pigment may be added to the composition.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of our copending applicationSer. No. 081,295, filed Oct. 2, 1979, now allowed.

BACKGROUND TO THE INVENTION

The invention relates to the use of a reactive diluent in common coatingcompositions made up of hydroxy-functional resins which are curable, bymeans of an aminoplast or phenolic resin, upon heating. Presently, lowboiling diluents are employed as solvents for coating compositions andare removed upon heating said compositions in the curing process.

SUMMARY OF THE INVENTION

The instant invention comprises standard coating mixtures ofhydroxy-functional resins in admixture with aminoplastic or phenoliccuring agents therefor and, as a reactive diluent, a liquid, polyglycolhemi-formal of the formula ##STR1## Preferred because of the decreasedamount of volatiles produced during the heat curing step are hemi-formaldiluents of the above formula having a normal boiling point greater than150° C. The diluents of the instant invention, surprisingly, may beformulated into heat-curable compositions which do not require thepresence of a catalyst such as a strong acid in order to effect reactionbetween the hydroxy-functional resin and the aminoplast or phenoliccuring agent. The invention composition differs from the solvent-basedcoatings previously employed in the art in that it may be permanentlyincorporated in the final coating instead of being evaporated out as iscommonly the case and the resultant coatings do not suffer losses intheir physical properties as might be expected.

The invention comprises a curable composition comprising component (A) xparts by weight of a hydroxyl-bearing polymer; about 0.05x to about 3.0xparts by weight, which represents y-moles of component (B) a liquid,polyglycol hemi-formal diluent of the formula ##STR2## wherein R is ahydrocarbyl group of 1 to about 20 carbon atoms, R' is independentlyeach occurrence hydrogen or methyl, and n is a positive number;component (C) an aminoplast or phenolic resole capable of curingcomponent (A) to a tack-free state, present in from about (0.20x+z) toabout (2.5x+5z) parts by weight, z being equal to y multiplied by theequivalent weight of component (C). Optionally, component (D), acatalytic amount of a strong acid or weak acid catalyst for the reactionbetween components (A) and (C), may be added, however such catalyst isnot necessary in order to adequately cure the instant composition. Theinvention further comprises the above composition which has been heatedat a temperature and for a length of time sufficient to cure same to atack-free finish. The invention composition optionally comprises apigment of the nature commonly employed in paints and othercompositions.

DETAILED DESCRIPTION OF THE INVENTION

Component (A) of the invention is suitably any hydroxyl-bearing polymerwhich is commonly cured with an aminoplast or phenolic resin to formfilms and coatings. Component (A) suitably has at least two andpreferably three or more free-hydroxyl groups. Such polymers are thefree-hydroxyl containing polyesters such as are obtained by condensingdi- or polycarboxylic acids with diols, glycols, triols or higherpolyols in such a fashion and ratios that free-hydroxyls remainunreacted for further curing by means of the aminoplast resin. Solidepoxy resins, such as extended diglycidyl ethers of bisphenols, forexample: ##STR3## wherein n>1, are also suitable as component (A).

Another class of polymers suitably employed as component (A) are thoseobtained by polymerization of the unsaturated portion of vinyl monomerswhich bear or may be modified to bear free-hydroxyl groups which areultimately pendant from the polyethylenic backbone. Examples of suchpolymers are poly(vinyl alcohols) which may be obtained by thehydrolysis of polymers derived from the polymerization of vinyl acetatewith or without other vinylic unsaturated comonomers, frompoly(hydroxyalkylacrylates) such as hydroxyethylacrylate andhydroxypropylacrylate with or without other comonomers andpoly(α,β-unsaturated acids) derived from the polymerization ofα,β-unsaturated monomeric acids with or without other comonomers or bythe polymerization and subsequent hydrolysis of esters thereof. Suchmonomeric acids are acrylic acid, methacrylic acid, itaconic acid,maleic acid, citraconic acid, cinnamic acid and the like.

Component (A) polymers are employed in some arbitrary amount, hereafterdesignated as x parts by weight.

Component (B) comprises about 0.05x to about 3.0x parts by weight,preferably about 0.10x to about 2.0x of a liquid polyglycol hemi-formalof the formula ##STR4## wherein R, R' and n are defined as above.

Preferably, Component (B) has a normal boiling point of about 150° C. orgreater. Because the hemi-formal is essentially the reaction product ofa polyglycol monoether with formaldehyde, the product may decompose intopolyglycol monoether and formaldehyde at higher temperatures, e.g.,temperatures of about 250° C. or more. This is not detrimental toperformance of the hemi-formal in the invented composition, however,measurements of the normal boiling point of such compounds may not bepossible because of this decomposition.

Component (C) is an aminoplast or phenolic resole resin, capable ofcuring component (A) to a tack-free state, and is unreactive in thecomposition under normal conditions but becomes reactive with component(A) at elevated temperatures on the order of 100° C.-250° C., preferably120° C.-200° C. for a time sufficient to create the desired tack-freestate, usually about 5-60 minutes or more. Suitable curing agents areaminoplast resins such as melamine-formaldehyde condensation products orurea-formaldehyde condensation products commonly available for thispurpose and phenolic resole resins derived from the condensation ofphenols and aldehydes and which are commonly used to cure thehydroxy-bearing solid epoxy resins previously described.

The quantity of component (C) to be employed is such that from about thesum of 0.20x+z up to about the sum of 2.5x+5z parts by weight of theaminoplast or phenolic resin are present in the invention composition, zbeing equal to y multiplied by the equivalent weight of component (C).The equivalent weights of aminoplast and phenolic resins are commonlyavailable from the manufacturers thereof. Preferably, component (C) ispresent in at least about the sum of 0.20x+1.25z and is more preferablyat least about the sum of 0.20x+1.5z. Preferably, it is present in lessthan about the sum of 2.5x+3z; and most preferably in less than aboutthe sum of 2.5x+2.5z.

As previously mentioned, it is preferred not to employ a catalyst in theinvented composition as adequate cure times and good handlingcharacteristics of the uncured resin, e.g., good pot life, etc. areobtained without use of a catalyst. However, no harm is caused by thepresence of a catalyst and one may optionally be employed. Typicalcatalysts are the strong acids such as organosulfonic acids or theiramine salts, sulfuric acid or its amine salts, zinc fluoroborate,phosphoric acid, boron trifluoride, (or its etherate), and the like.Also suitable are weak acid catalysts such as alkylphosphoric acid orchloroacetic acid. Also suitable are strong or weak acid ion-exchangeresins. The catalysts may be employed in amounts from 0.0005x to about0.05x part by weight, wherein x is as previously defined, as is alreadyknown in the art.

The curable composition of the invention is suitably prepared by simplymixing the components in any order at ambient temperature or slightlyelevated temperatures less than the temperature required for the curingreaction. The curable composition of the invention may suitably beheated to about 50° C.-75° C. without effecting a premature cure. Thisfacilitates handling, mixing and application of the inventioncomposition. If desired, standard pigments such as titanium oxides,chromium oxides, zinc oxides and the like may be added in suitableamounts to impart a desired color to the invention composition.Similarly, surfactants or wetting agents may optionally be added to thecomposition as is common in the art.

The invention composition is applied to a substrate by any suitablemeans to form a film or coating thereon and the film or coating is thenheated to the curing temperature by means commonly used in the art suchas a hot air oven, a bank of infrared heat lamps or the like.

SPECIFIC EMBODIMENTS

The following examples serve to illustrate the composition of theinvention, the curing and employment thereof for the preparation offilms and coatings. Unless otherwise designated, the term "parts" whenemployed herein means parts by weight.

EXAMPLE 1 Preparation of Hemi-formal

One mole (275 g) of the monomethyl ether of polypropylene glycol of theformula ##STR5## was combined with 91 percent paraformaldehyde (33.0 g,1 mole) in the presence of 0.6 g paratoluene sulfonic acid catalyst. Thereagents were mixed and heated to 100° C. with stirring. A clearsolution resulted. Filtration to remove unreacted paraformaldehydeproduced the desired hemi-formal of the formula ##STR6## in 98 percentpurity and about 94 percent yield.

EXAMPLE 2 Preparation of Coatings

The hemi-formal prepared above was combined with an acrylic resin and amelamine resin in the proportions indicated by Table I. The reactantswere mixed until homogeneous and the coating formulation applied in athin film to a preweighed aluminum panel. The panel was then reweighedand placed in a forced-air oven for 30 minutes at 150° C. The panel wasthen removed from the oven, cooled and reweighed. The difference (loss)in weight of the cured panels in percent is a measure of the volatilesin the composition. The percent volatiles is taken as a measure of theeffectiveness of the diluent's incorporation into the cured coatingcomposition.

                  TABLE I                                                         ______________________________________                                                                      Wt.                                                  Wt.                      Mel-  Wt.                                            Acrylic           Wt.    amine Cata-  %                                       Resin.sup.1       Solvent                                                                              resin.sup.2                                                                         lyst.sup.3                                                                           Vola-                              Run  (g)      Solvent  (g)    (g)   (g)    tiles                              ______________________________________                                                      Ex..sup.1                                                       1    2.75     hemi-    2.60   4.48  <0.002.sup.4                                                                         30.8                                             formal                                                          2    2.75     Ex..sup.1                                                                              2.60   5.60  <0.002 30.9                                             hemi-                                                                         formal                                                           3*  2.75     PGM.sup.5                                                                              2.60   4.98  0.04   33.9                               4    2.75     PGM.sup.5                                                                              2.60   6.23  0.04   31.9                               5    2.75     PGM.sup.5                                                                              2.60   7.48  0.04   33.9                               6    2.75     PGM.sup.5                                                                              2.60   6.23  --     39.3                               7    2.75     PGM.sup.5                                                                              2.60   7.48  --     39.5                                             Ethoxy-                                                         8    2.75     ethyl    2.18   1.48  --      50.85                                           Acetate                                                         ______________________________________                                         *Runs 3-8 are comparative examples.                                           .sup.1 The acrylic resin was a commercially available resin marketed as       Acryloid AT400.                                                               .sup.2 The melamine resin was trimethoxymethyl melamine having equivalent     weight of 86 g sold commercially as Cymel 325.                                .sup.3 pToluene sulfonic acid.                                                .sup. 4 Present only as an impurity from hemiformal production.               .sup.5 Monomethyl ether of polypropylene glycol of the approximate formul     ##STR7##                                                                 

EXAMPLE 3

The coatings prepared according to Example 2 were then tested. Whereapplicable in the succeeding examples the following test procedures wereemployed. Hardness was determined using a Tukon hardness tester and isreported as a Knoop hardness number. Reverse Impact was tested accordingto the procedures of ASTM D2794-69. Water resistance was determined byimmersing cured panels in boiling water for one hour and examining thecoating for damage such as blistering or delamination. Adhesion wastested according to ASTM D3359-74.

The coatings prepared in Example 2 above were tested according to thepreceding methods. The results are summarized in Table II.

                  TABLE II                                                        ______________________________________                                        Physical properties for                                                       coatings in Table I                                                                                 Reverse                                                        Knoop          Impact,  %                                              Run    Hardness       in-lbs   Adhesion                                       ______________________________________                                        1      6.4            >10,<20  95                                             2      13.5           >20,<30  100                                            3      17.3           <4       0                                              4      19.4           <4       2                                              5      16.6           <4       0                                              6      15.2           <4       99                                             7      12.6           <4       100                                            8      16.8           <4       10                                             ______________________________________                                    

EXAMPLE 4

A second sample of hemi-formal was prepared according to the procedureof Example 1 except that a strong acid resin was employed as thecatalyst. Removal by filtration resulted in a highly pure productuncontaminated with residual catalyst. Tables III and IV indicatecompositions and physical properties of the resulting cured coatingsafter formulation, curing and testing according to the proceduresemployed in Examples 2 and 3.

                  TABLE III                                                       ______________________________________                                                                           Wt.                                             Wt.                           Mel-                                            Acrylic               Wt.     amine %                                         Resin.sup.1           Solvent resin.sup.2                                                                         Vola-                                Run  (g)        Solvent    (g)     (g)   tiles                                ______________________________________                                        1    2.75       hemi-formal                                                                              2.60    4.48  29.4                                 2    2.75       "          2.60    5.60  28.6                                 3    2.75       "          2.60    6.72  29.3                                 ______________________________________                                         .sup.1 Acryloid® AT-400                                                   .sup.2 Cymel® 325                                                    

                  TABLE IV                                                        ______________________________________                                        Physical properties for                                                       coatings in Table III                                                                               Reverse                                                        Knoop          Impact,  %                                              Run    Hardness       in-lbs   Adhesion                                       ______________________________________                                        1      4.9            20       100                                            2      5.0            30       100                                            3      2.9            >20,<30  100                                            ______________________________________                                    

EXAMPLE 5

A coating composition was prepared utilizing an epoxy resin, amelamine/formaldehyde resin, a reactive diluent and a catalyst. Panelswere coated and cured according to the procedure of Examples 2 and 3.The results are contained in Tables V and VI.

                  TABLE V                                                         ______________________________________                                                                       Wt.                                                  Wt.                      Mel-  Wt.                                            Epoxy             Wt.    amine Cata- %                                        Resin.sup.1       Solvent                                                                              resin.sup.2                                                                         lyst.sup.3                                                                          Vola-                              Run   (g)     Solvent   (g)    (g)   (g)   tiles                              ______________________________________                                        1     1.35    Ethoxy-   3.50   0.15  0.007 72.0                                             ethyl                                                                         acetate                                                         2     1.35    PGM       3.50   4.43  0.007 30.8                               3     1.35     "        3.50   5.54  0.007 29.9                               4     1.35     "        3.50   6.65  0.007 26.6                                             hemi-                                                           5     1.35    formal    350    4.21  0.02  28.4                                             hemi-                                                           6     1.35    formal    3.50   5.26  0.02  26.6                               ______________________________________                                         .sup.1 A commercially available high molecular weight diglycidyl ether of     bisphenol A sold as DER® 667 epoxy resin.                                 .sup.2 Hexamethoxy methyl melamine, equivalent weight = 65 g, available a     Cymel® 303.                                                               .sup.3 p-Toluene sulfonic acid.                                          

                  TABLE VI                                                        ______________________________________                                        Physical properties for                                                       coatings in Table V                                                                                 Reverse                                                        Knoop          Impact,   %                                             Run    Hardness       in-lbs    Adhesion                                      ______________________________________                                        1      12.7           40        100                                           2      <2.8           >30,<40   100                                           3      5.3            >40       100                                           4      <2.8           40        100                                           5      11.0           >4,<10     99                                           6      17.0           >4,<10     99                                           ______________________________________                                    

EXAMPLE 6

A coating composition was prepared utilizing an epoxy resin, aurea-formaldehyde resin, a reactive diluent and a catalyst. Results arecontained in Tables VII and VIII.

                  TABLE VII                                                       ______________________________________                                                                      Wt.                                                                           Urea-                                                 Wt.                     Formal-                                                                              Wt.                                            Epoxy            Wt.    dehyde Cata- %                                        Resin.sup.1      Solvent                                                                              resin.sup.2                                                                          lyst.sup.3                                                                          Vola-                              Run   (g)     Solvent  (g)    (g)    (g)   tiles                              ______________________________________                                        1     2.34    EE-Ace-  4.35   1.64   --    58.2                                             tate/-                                                                        xylene                                                           2*   2.34    PGM      4.35   8.92   0.01  49.7                                3*   2.34     "       4.35   9.91   0.01  51.9                               4     2.34    hemi-    4.35   9.56   0.05  36.6                                             formal                                                          5     2.34    hemi-    4.35   10.76  0.05  36.3                                             formal                                                          6     2.34    hemi-    4.35   11.95  0.05  35.6                                             formal                                                          ______________________________________                                         *Cured at 175° C.                                                      .sup.1 A low melting resin of diglycidyl ether of Bisphenol A sold as         DER® 661 epoxy resin.                                                     .sup.2 A urea/formaldehyde resin sold commercially as Cargill® 2156       having equivalent weight of 59.                                               .sup.3 p-Toluene sulfonic acid.                                          

                  TABLE VIII                                                      ______________________________________                                        Physical properties for                                                       coatings in Table VII                                                                        Reverse                                                              Knoop    Impact,    Water    %                                          Run   Hardness in-lbs     Resistance                                                                             Adhesion                                   ______________________________________                                        1     4.8      >10,<20    5% blush,                                                                              100                                                                  blister                                             2     10.5      >4,<10    5% delam.                                                                              100                                        3     11.1      >4,<10    100% delam.                                                                            100                                        4     7.4      20         no effect                                                                               90                                        5     5.5      >20,<30    1% blush  90                                        6     4.8      20         2% blush  50                                        ______________________________________                                    

What is claimed is:
 1. A curable composition comprising:(A) x parts byweight of a hydroxyl-bearing polymer; (B) about 0.05x to about 3.0xparts by weight, which represents y-moles, of a liquid polyglycolhemi-formal diluent of the formula ##STR8## wherein R is a hydrocarbylgroup of 1 to about 20 carbon atoms, R' is independently each occurrencehydrogen or methyl, and n is a positive number; and (C) an aminoplast orphenolic resole resin, capable of curing component (A) to a tack-freestate, present in a quantity of from about (0.20x+z) to about (2.5x+5z)parts by weight, z being equal to y multiplied by the equivalent weightof said aminoplast or phenolic resole resin.
 2. The composition of claim1 wherein component (A) is selected from the group consisting offree-hydroxyl containing polyester, free-hydroxyl containing solid epoxyresins, and homo- copolymers of vinyl alcohol, hydroxy-alkylacrylatesand α,β-unsaturated acids.
 3. The composition of claim 1 whereincomponent (B) has an atmospheric boiling point of about 150° C. orgreater.
 4. The composition of claim 1 wherein in component (B), R' ismethyl in one or more occurrences.
 5. The composition of claim 1 whereinin component (B), R' is methyl in a majority of occurrences.
 6. Thecomposition of claim 1 wherein in component (B), n is equal to 4 orgreater.
 7. The composition of claim 1 wherein in component (B), R' eachoccurrence is methyl, n is equal to about 4 or greater and R is methyl.8. The composition of claim 1 wherein component (C) is amelamine-formaldehyde resin.
 9. The composition of claim 1 whereincomponent (C) is present in from about 0.20x+1.25z up to about 2.5x+3z,parts by weight.
 10. The composition of claim 1 additionally comprisinga strong or weak acid present in from about 0.0005x to about 0.05x partby weight.
 11. The composition of claim 1 which further comprises apigment.
 12. The composition of claim 1, 10 or 11 which has been heatedat a temperature and for a time sufficient to cure said composition to atack-free finish.